<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>监视属性-天气案例</title>
    <script type="text/javascript" src="../js/vue.js"></script>
</head>
<body>
<div id="root">
    <h2>今天天气很{{info}}</h2>
    <button @click="changeWeather">切换天气</button>

</div>
<script type="text/javascript">
    Vue.config.productionTip = false

    const vm = new Vue({
        el: "#root",
        data: {
            isHot: true
        },
        computed: {
            info() {
                return this.isHot ? "炎热" : "凉爽"
            }
        },
        methods: {
            changeWeather() {
                this.isHot = !this.isHot
            }
        },
        // watch: {
        //     isHot: {
        //         immediate: true, // 初始化时，让handler调用一下
        //         // 当isHot发生改变时，会调用handler
        //         handler(newValue, oldValue) {
        //             console.log(newValue, oldValue)
        //         }
        //     }
        // }
    })

    vm.$watch("isHot", {
        immediate: true, // 初始化时，让handler调用一下
        // 当isHot发生改变时，会调用handler
        handler(newValue, oldValue) {
            console.log(newValue, oldValue)
        }
    })
</script>

</body>
</html>